This record as markdown: /tools/alexgladkov-claude-in-mobile/system-open-url.md
What system_open_url does on Claude Mobile
AI agents invoke system_open_url to trigger actions in Claude Mobile. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
Why system_open_url is rated High
Opening a URL in a device browser is an Execute-category action: it triggers an external operation whose effects depend entirely on the URL argument. An attacker or misconfigured agent could navigate to malicious sites, trigger drive-by downloads, invoke deep links that launch apps or authorize OAuth flows, or exfiltrate data. It does not merely read data — it actively causes the device to perform an action.
From the tool's definition 'Open URL in device browser' — triggers an external operation (opening a URL) on a mobile device via browser automation
Risk signalsAdmin/system-level operation
Attacks that exploit this kind of access
The rule that runs system_open_url safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Claude Mobile, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For system_open_url, this is the rule to start with:
system_open_url stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Claude Mobile, apply this rule, and every system_open_url call is checked against it from then on.
Questions about system_open_url
Open URL in device browser. It is categorised as a Execute tool in the Claude Mobile MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Claude Mobile MCP server in PolicyLayer and add a rule for system_open_url: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Claude Mobile. Nothing to install.
system_open_url is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the system_open_url rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for system_open_url. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
system_open_url is provided by the Claude Mobile MCP server (alexgladkov/claude-in-mobile). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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